Chapter 12 The Cell Cycle long strand of DNA 1 Genome the complete collection of an organism s genetic information as linked genes in a a Humans have 27000 to 40000 genes with information to make all proteins a cell needs b A gene codes for a specific polypeptide or a trait 2 DNA is packaged into chromosomes a b Long stand of DNA in eukaryotic cells Large circular molecule in prokaryotes 3 Uncondensed DNA unwounded not during division a Condensed wrapped up for chromosomes 4 Microtubules hollow tubes or fibers needed for cell division 5 Cytoskeleton fibers hold structure of cell make sure things move where they need to go 6 Somatic cells all cells of the body except reproductive cells undergo mitosis a Diploid 2n have 2 sets of chromosomes i Humans have a total of 46 chromosomes and 23 homologous pairs 7 Gametes are the reproductive cells a Sperm and egg i Haploid N have a single set of chromosomes ii Humans total of 23 chromosomes 8 Types of chromosomes a Autosomes b Sex chromosomes i Most chromosomes homologues look alike and carry the same genes but could be different alleles versions of those genes We have 22 pairs or 44 autosomes i Humans and other mammals uses chromosomes to distinguish between the sexes We have one pair of sex chromosomes Males have X and Y females have two Xs An X chromosome does not have the same genes as a Y chromosome 9 A pair of homologous chromosomes have the same genes but may have different versions of those genes called alleles a For genes found on Autosomes i Diploid cell 2 copies of each gene 2 alleles ii Haploid cell 1 copy of each gene 10 Cell Division a Types of cell division i A parent cell splits into 2 daughter cells In mitosis daughter cells are identical ii iii In meiosis daughter cells are not identical 11 Roles of Mitosis Reproduction growth development repair 12 DNA must be replicated each cell must get a complete copy of the genome before division can occur 13 Replication of the DNA forms two sister chromatids connected at the centromere 14 The mitotic cell cycle a M Phase includes mitosis and cytokinesis b Interphase accounts for 90 of the cell cycle i G1 first gap centered on growth ii S Synthesis chromosomes are copied DNA Replication iii G2 second gap cell completes preparations for cell division M Phase Mitosis division of the nucleus Cytokinesis division of the cytoplasm 15 Stages of Mitosis a Prophase prometaphase metaphase anaphase telophase cytokinesis 16 Before mitosis late interphase chromosomes have been duplicated but are loosely packed a Centrosomes microtubule organization center have been duplicated and begin to organize microtubules into an aster 17 Prophase a Chromosomes are condensed with sister chromatids joined together at the centromeres i Nucleoli disappear ii Mitotic spindle forms iii Centrosomes separate from each other and move toward opposite ends 18 Prometaphase chromosomes a Nuclear envelope fragments microtubules from the spindle interact with the b Microtubules from each pole attach to one of two kinetochores i Kinetochores protein and chromosomal DNA at the centromere a Sister chromatids are arranged at the metaphase plate the imaginary plane equidistant between the two poles of the cell 19 Metaphase 20 Anaphase a Centromeres divide separating the sister chromatids sister chromatids are pulled to each end of the cell 21 How do chromosomes move Which end of the microtubules shortens a One hypothesis motor proteins at the kinetochore walk the attached chromosome along the microtubule toward the pole b Excess microtubule sections depolymerize 22 Telophase a Cell continues to elongate nonkineticore microtubules lengthen b Two nuclei begin to form from fragments of the parent cell s nuclear envelope c Chromatic starts to uncoil d Cytokinesis begins 23 Cytokinesis a In animals actin and myosin microfilaments instead of microtubules They wrap around the inside of the cell causing a cleavage furrow b In plants there is a cell wall they have to rebuild a wall and bring things to a metaphase plate 24 Evolution of Mitosis a Binary fission in Prokaryotes i One big circular chromosome has two origins of replication that go to either side then pinches inward into two daughter cells ii Diatoms dinoflagellates 25 Regulating the cell cycle a Different cells vary in the frequency and times of cell divisions i Skin cells divide frequently throughout life ii Liver cells can divide but only when needed iii Muscle and nerve cells do not appear to divide after they reach maturity 26 Molecular control systems a Chemical signals that reside in the cytoplasm appear to control the cycle i Fusion of cells if a cell that is in S phase is fused with a cell that is in G1 the G1 27 Cell cycle control system nucleus will begin S phase Internal clock Internal and external controls a b Checkpoint in the cell cycles is a critical control point where stop and go signals regulate the cycle 28 G1 checkpoint restriction point in mammalian cells a Go ahead signal completes the cell cycle and divides b No go ahead cells enter G0 i G0 is a non dividing state 1 Most adult human cells are in G0 a Liver cells may be reactivated by growth factors 29 Cyclin dependent kinases Cdks a Protein kinases activate and deactivate other proteins by phosphorylating them b Levels of kinases remains stable i Many require cyclin to become active 30 Cyclin levels increase during interphase then drop during mitosis a MPF maturation promoting factor or M Phase promoting factor i Triggers the cell s passage past the G2 checkpoint to M Phase ii Triggers break down of cyclin iii Stimulates fragmentation of the nuclear envelope 31 M phase checkpoint a Check that all the chromosomes are attached to spindle at metaphase plate before anaphase ensures that daughter cells do not have missing or extra chromosomes b Kinetochores that have not yet attached to spindle microtubules provide signal to delay anaphase i Keeps anaphase promoting complex inactive APC ii Active APC triggers breakdown of cyclin and inactivation of proteins holding 32 External stimuli sister chromatids together a Growth factors Proteins released by one group of cells that trigger other cells to divide b Platelet derived growth factors PDGF produced by platelet blood cells bind to tyrosine kinase receptors of fibroblasts a type of connective tissue cells c PDGF released in the vicinity of injury i Fibroblasts triggered to divide help wound heal 33 Density dependent inhibition a At high densities the